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 Main subject - jan/feb 2005
continuation: Sampling a decisive tool for seed quality assurance
Sampling in the seed flow
In practice, it is convenient to do the sampling during seed conditioning, during the bagging process, which can be done manually or using an automatic sampler, but always taking into consideration that in both cases, it is important that the whole section of the seed flow is evenly sampled. Several primary samples must be taken in regular intervals of time so that they can represent the seed lot.
Manual sampling or with instruments
In certain situations, with chaffy seeds, manual sampling is the only satisfactory method. The primary samples must be taken with the hands full of seeds randomly from different positions. It is necessary to have samples of the deepest layers of the recipient. The use of instruments is viable when the seeds slide easily.
Sampling in bulk
The difficulties for sampling seed in bulk will depend on the conditions that it is stored. If the depth of the container or place where the seed is stored is in the range of 2-5 meters, the use of an instrument, of compatible size, is necessary. However, the methods and mainly the precautions should be the same ones required for any sampling.
Sampling plants
A hectare of corn possesses 50 thousand plants and considering that the maximum area for field inspection is 50 hectares, we will have 2,5 million plants, which for obvious reasons, must be sampled. In the case of plants, the intensity of the sample involves the tolerance of the contaminants and a factor accept universally, consisting that the size of the sample must be in a way that if it is found three contaminants, and the field can still be harvested for seed. Thereby, considering a tolerance of 0,2% (2 contaminants in 1000 plants), we will have to sample 1,500 plants. Therefore, each plant sampled will represent 1,667 plants. As smaller gets the tolerance, larger will be the number of plants to be sampled.
Sampling in the laboratory
The submitted sample, received in the laboratory of seed analysis, usually, needs to be reduced to a work sample equal or larger than the size prescribed for each specie and test to be accomplished.
The submitted sample, after being well mixed, it goes through successive divisions, using methods and specific instruments, in order to obtain the working sample.
Samples copies and sub-samples should be removed, independently of the submitted sample, being the remainder again homogenized, before other sample or sub sample is removed.
Importance
In order to have an idea of the sampling importance, let us use the germination test.
Considering that a lot of soybean seeds has 20 ton. and that, six seeds weigh one gram, that lot will have 120 millions seeds. As mentioned, in the text, we will not test all of the seeds, however we will do a sampling in a way that the seeds used in the germination test represent the entire lot. Considering that the germination test uses a working sample of 400 seeds, the result obtained in the germination test will represent the 120 million seeds of the lot. In case the sampling is not correctly accomplished, that relationship will not be true, therefore, with loss for everyone.
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